1. Field of the Invention
The present invention relates to a fluid-filled elastic mount such as an engine mount for an automotive vehicle, and in particular to such elastic mounts which effectively damp or isolate vibration in a wide frequency range.
2. Related Art Statement and Problems Solved by the Invention
A mounting device such as an engine mount for an automobile is required to effectively damp or isolate vibration in a wide frequency range which essentially includes a comparatively low frequency range.
Recently there has been proposed a "fluid-filled" elastic mount, as one of such mounting devices, which includes (a) a first and a second support member which are disposed opposite to each other in a load-receiving direction in which a vibrational load is applied to the elastic mount, (b) an elastic body interposed between the first and second support member, for elastic connection of the first and second support member, (c) a closure member secured to the second support member and cooperating with at least the elastic body to define a fluid chamber filled with a non-compressible fluid, the closure member including a flexible portion, (d) a partition member for dividing the fluid chamber into a pressure-receiving chamber formed on the side of the first support member, and an equilibrium chamber formed on the side of the closure member; and (e) a restricted passage for restricted fluid communication between the pressure-receiving and equilibrium chambers. The elastic mount of this type is disclosed in German Patent Applications laid-open under OLS No. 2905090 and OLS No. 2905091.
In the elastic mount constructed as indicated above, the vibration with which the non-compressible fluid in the restricted passage resonates is effectively damped. Stated differently, the restricted passage is constructed or "tuned" so that the fluid therein resonates with vibration having a predetermined frequency, specifically in a comparatively low frequency range. Thus, the comparatively low frequency vibration is effectively damped by this elastic mount.
Although the above-indicated type elastic mount is capable of effectively damping the comparatively low frequency vibration based on the resonant response of the fluid in the restricted passage, the mount is not capable of sufficiently damping or isolating vibration in different frequency ranges from the comparatively low range, particularly a range higher than the comparatively low range. When the comparatively high frequency vibration is applied to the elastic mount, the fluid in the restricted passage becomes rigid, whereby the fluid becomes unable to flow between the pressure-receiving and equilibrium chambers through the restricted passage, which leads to rather lowering the vibration absorbing capability of the elastic mount.
Another fluid-filled elastic mount has been proposed in European Patent Application laid-open under EP-A No. 0040290 and U.S. Pat. No. 4,511,126. The elastic mount has, in addition to the above-indicated elements (a) through (f), accommodation means for accommodating a pressure difference between the pressure-receiving and equilibrium chambers, the accommodation means including a movable member which is displaceable or deformable a predetermined distance or amount due to the pressure difference.
In this type elastic mount, the accommodation means is constructed or "tuned" so that vibration with a predetermined frequency, specifically a comparatively high frequency vibration, is effectively isolated based on deformation or displacement of the movable member due to a pressure difference produced between the pressure-receiving and equilibrium chambers. The frequency of the vibration isolated with the movable member may be determined to be higher than the comparatively low frequency of the vibration damped with the restricted passage. Thus, the comparatively high frequency vibration can be isolated by this elastic mount.
Thus, the fluid-filled elastic mount of the above-indicated type effectively damps or isolates the vibrations in the two different frequency ranges, namely, the low frequency range associated with the restricted passage and the comparatively high frequency range associated with the movable member, but suffers from the problem of being incapable of sufficiently isolating vibration in a frequency range higher than the two different ranges covered by the conventional elastic mount. An upper limit of the comparatively high frequency range associated with the movable member is not more than about 150-200 Hz, and accordingly vibration with a frequency higher than about 150-200 Hz is not effectively isolated based on the movement of the movable member of the conventional elastic mount.